Drop Down Menu Help

I made a drop down menu in a search feature. The search feature works great, except I wanted to add an extra feature to it...

What I want is if a user selects GAME in the drop down, I wish to make a new drop down menu appear displaying categories... How can I do this? I've googled, but received no answer.

Thanks...

<?PHP


echo"<form action='' method='get'>
Term: <input type='text' value='' name='search' /> <br /><br />
Search by: <br /><select size='1' name='by'>
<option value='game'>Game</option>
<option  value='item'>Item</option>
<option value='name'>User</option>
<option  value='usershop'>Usershop</option></select>";


//If User Selects GAME display Categories below
echo"<br />In Category: <select size='1' name='searchcat'>
<option value='All' selected='selected'>All</option>";
$catquery=run_query("SELECT * FROM phpqa_cats");
while ($catlist= mysql_fetch_array($catquery)) echo  "<option value='$catlist[0]'>$catlist[1]</option>";
//End Display Categories
?>

</select><br /><br />
<input type='submit' value='search' name='action' />
<br /><br />
</form>

PHP:

 

Your probably looking for a Dynamic Select box ?

Either that or look into using JQuery or prototype to create the second select box using some ajax calls.